事件委托小demo(原生版)

<style type="text/css">
        body, div, span {
            margin: 0;
            padding: 0;
            font-family: "5FAE8F6F96C59ED1", Helvetica, sans-serif;
            font-size: 14px;
        }

        html, body {
            width: 100%;
            height: 100%;
            overflow: hidden;
        }

        #box {
            position: absolute;
            left: 50%;
            top: 50px;
            margin-left: -50px;
            width: 100px;
            height: 30px;
            line-height: 30px;
            text-align: center;
            border: 1px solid #2489ce;
        }

        #mark {
            position: absolute;
            top: 30px;
            left: -1px;
            width: 300px;
            height: 100px;
            line-height: 100px;
            text-align: center;
            background: #ffe470;
            border: 1px solid #2489ce;
        }
    </style>

<div id="box">
    <span>购物车</span>
    <div id="mark" style="display: none;">查看购物车中的详细信息</div>
</div>

<script type="text/javascript">
    var mark = document.getElementById("mark");

    document.body.onclick = function (e) {
        e = e || window.event;
        e.target = e.target || e.srcElement;

        //->如果点击的是#box或者是#box下的span,我们判断mark是否显示,显示的话让其隐藏,反之隐藏的话让其显示
        if (e.target.id === "box" || (e.target.tagName.toLowerCase() === "span" && e.target.parentNode.id === "box")) {
            if (mark.style.display === "none") {
                mark.style.display = "block";
            } else {
                mark.style.display = "none";
            }
            return;
        }

        //->如果事件源是#mark，不进行任何的操作
        if (e.target.id === "mark") {
            return;
        }

        //->以上都不是的话，我们直接让#mark隐藏
        mark.style.display = "none";
    };
</script>